Medical devices such as intravascular and intracardiac catheters are commonly used for a variety of medical procedures, such as in cardiovascular, neurologic, endoscopic, neurovascular, renal, and other applications. For example, these steerable devices may be used in minimally invasive procedures such as cardiac ablation, mapping, stent delivery, and imaging. In performing procedures such as these, it is often desirable, if not essential, that the catheter is steerable in order to navigate the catheter through the patient's vasculature to the desired treatment location. For medical devices that are themselves not steerable, a steerable catheter sheath may be used to guide the medical device to a treatment desired treatment location.
Steerable sheaths and steerable catheters may include multiple longitudinal lumens. In the case of a steerable catheter, for example, the catheter body may include a major or central lumen through which a push rod, rigid or semi-rigid guidewire lumen, or shaft may be passed. In the case of a steerable sheath, for example, the sheath may include a major or central lumen through which a second device or catheter may be passed. In both cases, the catheter or sheath may include one or more minor lumens for one or more pull wires used for steering.
Manufacturing methods for steerable catheters and sheaths have improved over the years. Many such devices that once required tedious hand assembly or time-intensive ram extrusion can now be produced using extrusion techniques that allow for multilayer extrusion of a device. For example, a sheath may be produced with an inner layer consisting of a lubricious material such as polytetrafluoroethylene (PTFE), a middle layer consisting of a braided steel matrix for strength and torque transmission, and an outer layer consisting of a thermoplastic or similar material. Although the manufacturing process is becoming more efficient, there are still several aspects of steerable catheter and sheath production that are inefficient and costly.
One example of a limitation in steerable catheter and sheath production is the creation of the minor lumens. A thin layer of PTFE, for example, having a wall thickness of about 0.025 mm (approximately 0.001 inch), is commonly used for the minor lumens. Although this material is valued for its low coefficient of friction, it is not very rigid and easily collapses during the manufacturing process, particularly when used for the small-diameter minor lumens. To prevent collapse, a rigid mandrel is inserted into each minor lumen to prevent collapse during braiding, reflow, or other manufacturing steps. Although effective in maintaining patency of the minor lumens, the use of mandrels adds cost and complexity to the manufacturing process.
Additionally, extrusion may be used to manufacture steerable catheters and sheaths. However, these multi-lumen devices are commonly produced using a discrete extrusion and/or fusing method, in which a usable length of catheter body or sheath, for example, less than six feet (such as around three feet), is extruded at a time. Each length of catheter body or sheath may be manufactured in a series of steps or “passes.” As an example, a polymer tube is extruded and cut to a desired length, creating discrete polymer tubes. Each tube is then slid over a length of mandrel, and a stainless steel braided wire mesh is overlayed over each discrete tube. Then, another polymer tube is slid over the mandrel, first polymer tube, and mesh layer, and the whole assembly is heated in an oven to fuse the materials together and create discrete lengths of catheter or sheath body. Undergoing each step for a discrete length of catheter or sheath is inefficient and adds increased labor requirements and operational costs.
It is therefore desired to provide efficient and cost-effective methods of manufacturing steerable catheter bodies and steerable sheaths. In one aspect, it is desirable to provide a method of manufacturing these multi-lumen devices without the need for a mandrel, which incurs additional production cost. In another aspect, it is desirable to provide a method of manufacturing these multi-lumen devices using an efficient extrusion process.